An LED, as a lighting element, has the advantages of low power, high lighting efficiency, favorability to energy conservation, long service life, and avoidance of pollution, so is extensively used in our daily life. By connecting a plurality of LEDs in parallel or in series, an LED tubular lamp can be constructed for lighting purpose. Such LED tubular lamp saves more energy as compared with the conventional fluorescent lamps, and thus gradually substitutes for the latter. LEDs generate heat when operating, and therefore the lamp composed of plural LEDs is likely to have highly accumulated heat during lighting. The accumulated heat, when not dissipated timely, can cause light attenuation and decrease lighting efficiency and illumination of the LEDs.
A conventional energy-saving LED tubular lamp is depicted in FIGS. 1 and 2. It comprises a lamp head 1 mounted around a lampshade 2 and a metal profile 5 that have been combined. The metal profile 5 is a hollow extrusion, and the lampshade 2 is attached to its bottom. The combined lampshade 2 and metal profile 5 enclose a printed circuit board 3, which has a bottom facing the lampshade 2 provided with a plurality of LEDs 4, and is inlaid to receiving recesses 51 formed by a pair of flanges 512 bilaterally formed at a bottom of the metal profile 5.
In the foregoing conventional energy-saving LED tubular lamp, the printed circuit board 3 is installed between the receiving recesses 51 of the metal profile 5. The heat generated by the LEDs in operation is on one hand dissipated through the lampshade 2, and on the other hand transferred to the printed circuit board 3 to be then transferred to the entire metal profile 5 through a binding surface 511 of the metal profile 5 that closely contacts the printed circuit board 3, so that the heat generated by the LEDs can dissipated. However, in practical applications, since the lampshade and the metal profile are combined in a closed manner and the lampshade is made of a material with low thermal conductivity, e.g. plastic, the heat generated by the LEDs in operation is likely to be accumulated inside the lampshade and can only conductively dissipated outside the lamp though the contact between the printed circuit board 3 and the metal profile 5. Theoretically, the metal profile is made of a high thermal conductive and dissipating material that serves to dissipate the heat generated by the LEDs from the printed circuit board. However, in the conventional heat-dissipation structure of the LED lamp, the printed circuit board 3 is positioned below the metal profile 5 and only supported by the two flanges 512 of the metal profile 5 to be held in the receiving recesses 51. Thus, by gravity, the printed circuit board 3 is unlikely to remain in close contact with the binding surface 511 of the metal profile 5. As a result, the real thermal conductive area is limited to the very small surfaces of the flanges 512 of the metal profile for propping up the printed circuit board. This significantly reduces the possibility of greatly and rapidly dissipating heat through the contact between the printed circuit board 3 and the metal profile 5. In addition, since the printed circuit board has its bottom provided with the plural LEDs, under the double load from the weight and the gravity, the printed circuit board has to be made with a proper thickness, so the conventional printed circuit board is typically as thick as 0.8 mm. Nevertheless, a printed circuit board of such thickness is unfavorable to heat transmission and thus has inferior heat dissipation efficiency, causing the LEDs to have gradually lowered light efficiency and premature aging. All these reasons bring difficulties to extensive applications of the conventional LED tubular lamp.